No abstract

In this study, we investigated the in vitro and in vivo biologic activity of bone morphogenetic protein 2 (BMP-2) released from four sustained delivery vehicles for bone regeneration. BMP-2 was incorporated in 1) a gelatin hydrogel, 2) poly(lactic-co-glycolic acid) (PLGA) microspheres embedded in a gelatin hydrogel, 3) microspheres embedded in a poly(propylene fumarate) (PPF) scaffold and 4) microspheres embedded in a PPF scaffold surrounded by a gelatin hydrogel. A fraction of the incorporated BMP-2 was radiolabeled with 125 I to determine its in vitro and in vivo release profiles. The release and bioactivity of BMP-2 were tested weekly over a period of 12 weeks in preosteoblast W20-17 cell line culture and in a rat subcutaneous implantation model. Outcome parameters for in vitro and in vivo bioactivity of the released BMP-2 were alkaline phosphatase (AP) induction and bone formation, respectively. The four implant types showed different in vitro release profiles over the 12-week period, which changed significantly upon implantation. The AP induction by BMP-2 released from gelatin implants showed a loss in bioactivity after 6 weeks in culture, while the BMP-2 released from the other implants continued to show bioactivity over the full 12-week period. Micro-CT and histological analysis of the delivery vehicles after 6 weeks of implantation showed significantly more bone in the microsphere/PPF scaffold composites (implant 3, p < 0.02). After 12 weeks, the amount of newly formed bone in the microsphere/PPF scaffolds remained significantly higher than in the gelatin and microsphere/gelatin hydrogels (p < 0.001), however there was no statistical difference compared to the microsphere/PPF/gelatin composite. Overall, the results from this study show that BMP-2 could be incorporated into various bone tissue engineering composites for sustained release over a prolonged period of time with retention of bioactivity.

Background Spondylodiscitis is a spinal infection affecting primarily the intervertebral disk and the adjacent vertebral bodies. Currently many aspects of the treatment of pyogenic spondylodiscitis are still a matter of debate. Purpose The aim of this study was to review the currently available literature systematically to determine the outcome of patients with pyogenic spondylodiscitis for conservative and surgical treatment strategies. Methods A systematic electronic search of MEDLINE, EMBASE, Cochrane Collaboration, and Web of Science regarding the treatment of pyogenic spondylodiscitis was performed. Included articles were assessed on risk of bias according the Cochrane Handbook for Systematic Reviews of Interventions, and the quality of evidence and strength of recommendation was evaluated according the GRADE approach. Results 25 studies were included. Five studies had a high or moderate quality of evidence. One RCT suggest that 6 weeks of antibiotic treatment of pyogenic spondylodiscitis results in a similar outcome when compared to longer treatment duration. However, microorganism-specific studies suggest that at least 8 weeks of treatment is required for S. aureus and 8 weeks of Daptomycin for MRSA. The articles that described the outcome of surgical treatment strategies show that a large variety of surgical techniques can successfully treat spondylodiscitis. No additional long-term beneficial effect of surgical treatment could be shown in the studies comparing surgical versus antibiotic only treatment. Conclusion There is a strong level of recommendation for 6 weeks of antibiotic treatment in pyogenic spondylodiscitis although this has only been shown by one recent RCT. If surgical treatment is indicated, it has been suggested by two prospective studies with strong level of recommendation that an isolated anterior approach could result in a better clinical outcome.

Aiming to achieve suitable polymeric biomaterials with controlled physical properties for hard and soft tissue replacements, we have developed a series of blends consisting of two photo-cross-linkable polymers: polypropylene fumarate (PPF) and polycaprolactone fumarate (PCLF). Physical properties of both un-cross-linked and UV cross-linked PPF/PCLF blends with PPF composition ranging from 0% to 100% have been investigated extensively. It has been found that the physical properties such as thermal, rheological, and mechanical properties could be modulated efficiently by varying the PPF composition in the blends. Thermal properties including glass transition temperature (T g) and melting temperature (T m) have been correlated with their rheological and mechanical properties. Surface characteristics such as surface morphology, hydrophilicity, and the capability of adsorbing serum protein from culture medium have also been examined for the cross-linked polymer and blend disks. For potential applications in bone and nerve tissue engineering, in vitro cell studies including cytotoxicity, cell adhesion, and proliferation on cross-linked disks with controlled physical properties have been performed using rat bone marrow stromal cells and SPL201 cells, respectively. In addition, the role of mechanical properties such as surface stiffness in modulating cell responses has been emphasized using this model blend system.

Bone regeneration is a complex process regulated by a large number of bioactive molecules. Many growth factors and cytokines involved in the natural process of bone healing have been identified and tested as potential therapeutic candidates to enhance the regeneration process. Although many of these studies show an enhancement of the bone regeneration process by a single drug therapy, in vivo bone regeneration is the result of a complex interplay between the applied growth factor and various endogenous produced growth factors. To investigate these growth factor interactions, various studies have investigated the effect of growth factor combinations on bone regeneration. This review provides an overview of the growth factor and cytokine combinations tested in translational bone regeneration studies and shows that their interaction may result in an enhancement or inhibition of bone formation.

In bone tissue engineering, growth factors are widely used. Bone morphogenetic proteins (BMPs) and vascular endothelial growth factor (VEGF) are the most well-known regulators of osteogenesis and angiogenesis. We investigated whether the timing of dual release of VEGF and BMP-2 influences the amount of bone formation in a large-animal model. Poly(lactic-co-glycolic acid) (PLGA) microparticles (MPs) were loaded with BMP-2 or VEGF to create sustained-release profiles, and rapidly degrading gelatin was loaded with either growth factor for fast-release profiles. To study in vivo osteogenicity, the two delivery vehicles were combined with biphasic calcium phosphate (BCP) scaffolds and implanted in 10 Beagle dogs for 9 weeks, at both ectopic (paraspinal muscles) and orthotopic sites (critical-size ulnar defect). The 9 ectopic groups contained combined or single BMP/VEGF dosage, in sustained-or fast-release profiles. In the ulnae of 8 dogs, fast VEGF and sustained BMP-2 were applied to one leg, and the other received the opposite release profiles. The two remaining dogs received bilateral control scaffolds. Bone growth dynamics was analyzed by fluorochrome injection at weeks 3, 5, and 7. Postoperative and posteuthanization X-rays of the ulnar implants were taken. After 9 weeks of implantation, bone quantity and bone growth dynamics were studied by histology, histomorphometry, and fluorescence microscopy. The release of the growth factors resulted in both enhanced orthotopic and ectopic bone formation. Bone formation started before 3 weeks and continued beyond 7 weeks. The ectopic BMP-2 fast groups showed significantly more bone compared to sustained release, independent of the VEGF profile. The ulna implants revealed no significant differences in the amount of bone formed. This study shows that timing of BMP-2 release largely determines speed and amount of ectopic bone formation independent of VEGF release. Furthermore, at the orthotopic site, no significant effect on bone formation was found from a timed release of growth factors, implicating that timed-release effects are location dependent.

Following an endochondral approach to bone regeneration, multipotent stromal cells (MSCs) can be cultured on a scaffold to create a cartilaginous callus that is subsequently remodeled into bone. An attractive scaffold material for cartilage regeneration that has recently regained attention is decellularized cartilage-derived matrix (CDM). Since this material has shown potential for cartilage regeneration, we hypothesized that CDM could be a potent material for endochondral bone regeneration. In addition, since decellularized matrices are known to harbor bioactive cues for tissue formation, we evaluated the need for seeded MSCs in CDM scaffolds. In this study, ectopic bone formation in rats was evaluated for CDM scaffolds seeded with human MSCs and compared with unseeded controls. The MSC-seeded samples were preconditioned in chondrogenic medium for 37 days. After 8 weeks of subcutaneous implantation, the extent of mineralization was significantly higher in the MSC-seeded constructs versus unseeded controls. The mineralized areas corresponded to bone formation with bone marrow cavities. In addition, rat-specific bone formation was confirmed by collagen type I immunohistochemistry. Finally, fluorochrome incorporation at 3 and 6 weeks revealed that the bone formation had an inwardly directed progression. Taken together, our results show that decellularized CDM is a promising biomaterial for endochondral bone regeneration when combined with MSCs at ectopic locations. Modification of current decellularization protocols may lead to enhanced functionality of CDM scaffolds, potentially offering the prospect of generation of cell-free off-the-shelf bone regenerative substitutes.

The ideal biomaterial for the repair of bone defects is expected to have good mechanical properties, be fabricated easily into a desired shape, support cell attachment, allow controlled release of bioactive factors to induce bone formation, and biodegrade into nontoxic products to permit natural bone formation and remodeling. The synthetic polymer poly(propylene fumarate) (PPF) holds great promise as such a biomaterial. In previous work we developed poly(DL-lactic-co-glycolic acid) (PLGA) and PPF microspheres for the controlled delivery of bioactive molecules. This study presents an approach to incorporate these microspheres into an injectable, porous PPF scaffold. Model drug Texas red dextran (TRD) was encapsulated into biodegradable PLGA and PPF microspheres at 2 microg/mg microsphere. Five porous composite formulations were fabricated via a gas foaming technique by combining the injectable PPF paste with the PLGA or PPF microspheres at 100 or 250 mg microsphere per composite formulation, or a control aqueous TRD solution (200 microg per composite). All scaffolds had an interconnected pore network with an average porosity of 64.8 +/- 3.6%. The presence of microspheres in the composite scaffolds was confirmed by scanning electron microscopy and confocal microscopy. The composite scaffolds exhibited a sustained release of the model drug for at least 28 days and had minimal burst release during the initial phase of release, as compared to drug release from microspheres alone. The compressive moduli of the scaffolds were between 2.4 and 26.2 MPa after fabrication, and between 14.9 and 62.8 MPa after 28 days in PBS. The scaffolds containing PPF microspheres exhibited a significantly higher initial compressive modulus than those containing PLGA microspheres. Increasing the amount of microspheres in the composites was found to significantly decrease the initial compressive modulus. The novel injectable PPF-based microsphere/scaffold composites developed in this study are promising to serve as vehicles for controlled drug delivery for bone tissue engineering.